Simplify the following expression: ${3(-y+7)-3(5-3y)}$
Answer: Distribute the ${3}$ into the first set of parentheses: $ {3(}\gray{-y+7}{)} - 3(5-3y) $ $ {-3y+21} - 3(5-3y) $ Distribute the ${-3}$ into the parentheses: $ -3y+21 {-3(}\gray{5-3y}{)} $ $ -3y+21 {-15+9y} $ Rewrite the expression to group the ${y}$ terms and numeric terms: $ {-3y + 9y} + {21 - 15}$ Combine the ${y}$ terms: $ {6y} + {21 - 15}$ Combine the numeric terms: $ {6y} + {6}$ The simplified expression is $6y+6$